1. Field of the Invention
The present invention relates to a semiconductor production apparatus and a target device for use in the semiconductor production apparatus.
2. Description of the Related Art
FIG. 1 schematically shows a sputtering apparatus which is conventionally used in production of semiconductors. In FIG. 1, the sputtering apparatus 1 has a chamber 2 for maintaining therein an atmosphere of a predetermined reduced pressure. The chamber 2 accommodates a target 3 and a semiconductor wafer 4 which is supported by a support member 5 opposite the target 3.
In operation, Ar gas is introduced into the chamber 2 through a valve 6a while the chamber 2 is continuously evacuated through the valve 6b so that the atmosphere in the chamber 2 is held at a pressure level which generally ranges between 0.13 and 6.7 Pa (1.times.10.sup.-3 Torr to 5.times.10.sup.--2 Torr). The target 3, a cathode, is supplied with D.C. power or high-frequency A.C. power from a power supply 7, so that a glow discharge is commenced in the chamber 2. As a result of the glow discharge, the Ar gas is ionized to Ar+ ions which are attracted to and impinge upon the target 3, which is biased to a negative potential, whereby the target 3 is sputtered. Particles 8 of the material of the target 3, coming out the target 3 as a result of the sputtering are deposited on the semiconductor wafer 4 which opposes the target 3. The target 3 is heated to, for example, 200 to 300.degree. C. as a result of the sputtering, so that it must be cooled by, for example, water from the side 9 thereof opposite to the wafer 4. The mean free path of the particles 8 coming out the target 3 is comparatively small and most of the particles 8 collide with one another and are scattered before reaching the semiconductor wafer 4. This type of sputtering apparatus therefore exhibits superior detouring in the particles 8, as well as high degree of uniformity of thickness of the film formed by the sputtering.
FIGS. 2(a) to 2(d) are schematic illustrations of the target 3, e.g., a copper target, used in the sputtering apparatus of the type described, in different steps of a process for forming the target 3. The target 3 is formed by bonding a metal target 10 to a backing plate 12 through a solder 11, e.g., a solder composed of 95 wt% of Sn and 5 wt% of Ag (see FIG. 2(a)). More specifically, the metal target 10 and the backing plate 12 are superposed through the intermediary of the solder 11. Then, the solder 11 is melted by a suitable heating means such as a heater (not shown) to become molten solder 11a (see FIG. 2(c)) and then the solder 11 is solidified to become solidified solder 11b (see FIG. 2(d)), whereby a target 3 is prepared as shown in FIG. 2(b).
FIG. 3 is a graph showing the distributions of concentrations of metal elements diffused in the region around the interfaces between the solder 11 and the metal target 10 or the backing plate 12. In this Figure, the ordinate represents the concentrations of the metal elements, while the abscissa represents the distance from the interface A. As will be seen from this Figure, the metal diffused by the heat during melting of the solder 11 causes the metal elements to diffuse and form alloy layers such as Cu-Sn layer B and Cu-Sn-Ag layer C in the region around the interface A.
Thus, the target 3 shown in FIG. 2(a) has a Cu-Sn-Ag layer C formed on each side of the solder 11 and a Cu-Sn layer B formed on the side of each Cu-Sn-Ag layer C opposite to the solder 11, as schematically shown in FIG. 4. In general, Cu-Sn alloys exhibit impractically small elongation, i.e., large brittleness, when the Sn content is 25wt% or greater, as will be seen from FIG. 8 which shows mechanical properties of this type of alloys. In FIG. 8, curves A, B and C show tensile strength, elongation and hardness, respectively. Due to the large brittleness, the Cu-Sn layer tends to crack as denoted by 13 in FIG. 5 as a result of thermal expansion of the target 3 and thermal impact during sputtering.
Such a crack 13 formed in the Cu-Sn layer B may undesirably allow the metal target 10 to come off the backing plate 12. In addition, when the sputtering of the target 3 is continued after separation of the metal target 10, impurities are undesirably incorporated into the semiconductor wafer 4.